The present invention relates to a controlling apparatus for an engine including an exhaust gas recirculation apparatus, and more particularly to an engine controlling apparatus which predicts occurrence of low-speed pre-ignition that occurs under low-speed and high-load conditions.
Many engines mounted on vehicles include an exhaust gas recirculation apparatus. An exhaust gas recirculation apparatus recirculates part of exhaust gas that is discharged from a combustion chamber of an engine toward the atmosphere through an exhaust passage, into an intake passage, whereby the combustion temperature in the combustion chamber is lowered, and emission of nitrogen oxides (NOx) contained in the exhaust gas is suppressed.
A technique is available in which an exhaust gas recirculation apparatus reduces abnormal combustion in a combustion chamber of an engine by using exhaust gas recirculated into an intake passage (hereinafter, such exhaust gas is referred to as “recirculation gas”).
In the technique disclosed in JP-A-62-131961, for example, an outlet leading to an intake passage for recirculation gas is placed in the vicinity of a combustion chamber, and the direction of the outlet is set so that the recirculation gas introduced into the combustion chamber flows along the inner peripheral wall of a cylinder. The recirculation gas which swirls in the combustion chamber along the inner peripheral wall of the cylinder forms an annular recirculation gas layer in a portion near the inner peripheral wall. In a middle portion of the combustion chamber where a spark plug is placed, therefore, the exhaust gas concentration is relatively lowered to enhance and the ignition performance, and, in an outer peripheral portion of the combustion chamber, a phenomenon which is so-called “knocking,” and in which the exhaust gas concentration in the vicinity of the inner peripheral wall of the cylinder is raised, and the end gas is auto-ignited is prevented from occurring.
JP-A-2010-84619 discloses a technique in which occurrence of pre-ignition is predicted by using a prediction formula called the Livengood-Wu integral expression.
Usual pre-ignition is caused by a phenomenon in which deposit accumulated in a combustion chamber is peeled off from the wall surface of a cylinder, and then exposed to combustion to glow, and the glowing deposit becomes the source of auto-ignition. On the other hand, it is said that low-speed pre-ignition is caused by above-described deposit or another phenomenon in which droplets of lubricating oil scattering from the inner peripheral wall of a cylinder ignite in accordance with a temperature rise of the interior of a combustion chamber, and then the droplets function as pilot fire to cause a gas mixture to auto-ignite.
As a technique for preventing usual pre-ignition from occurring, a technique in which the ignition timing is delayed is employed. On the other hand, examples of a technique for preventing low-speed pre-ignition from occurring are a technique in which the intake air temperature is lowered, and that in which the oxygen concentration in the gas mixture is reduced. When the technique in which the intake air temperature is lowered is employed, however, there is a case where a significant output reduction is caused depending on driving conditions. When, in the configuration of JP-A-62-131961, the amount of the recirculation gas introduced into the intake air is increased in order to reduce the oxygen concentration in the gas mixture, for example, the temperature in the combustion chamber is raised, and therefore there may occur an opposite case where pre-ignition is induced. Consequently, there is a limit to the increase of the introduction amount of the recirculation gas.
In the pre-ignition prediction which is described in JP-A-2010-84619, based on whether the auto-ignition index based on factors of the cylinder pressure and temperature in the compression stroke exceeds a predetermined threshold or not, it is determined whether pre-ignition occurs before the ignition timing, i.e., the ignition target crank angle or not.
In the prediction formula, however, the amount of fuel adhering to the inner peripheral wall of a cylinder, and the introduction amount of the recirculation gas are not considered, and therefore there may arise a case where occurrence of low-speed pre-ignition cannot be correctly predicted.